Portal to XI to R/3

Currently we have an interface in Production and the developer who has created this interface is not any more with our company.

We are encountering some problems with this interface(basically it is not working) and I am trying to understand this interface.

What I have understood so for is, On the portal side we are entering the SSN and it travels thru xi and goes to the Banking System and banking system returns back the credit History score to the Portal.

The banking system has been connected thru an Sync Receiver HTTP Adapter.

But I am confused how the Portal should have been connected to XI? I do see an HTTP Async Receiver Adapter between XI and Portal? My friend in the team says that Portal will not be normally connected to the XI, the request from portal will first go to an R/3 System then the R/3 will talk to XI? So confused, any ideas?

Thanks.